1. Industrial Useful Field
This invention relates to an improvement of an automatic transmission, in which a four-element, two-stage stator reversing type torque converter is combined with a speed changer having first and second planetary gears sharing one planetary carrier in common and a clutch or brake for controlling the planetary gear.
2. Prior Art and Its Problem
Generally, in an automatic transmission for use in an automobile, a torque converter and a speed changer are combined. There are several types of speed changer, and a speed changer using a clutch will be accompanied by the following problem.
Namely, in case when a gear ratio of speed changer is to be adjusted finely according to a type of car, a gear ratio of only a part of planetary gears can not be changed and the entire speed changer must be newly designed again, so that a fine adjustment of gear ratio can not be carried out easily.
Further, an engine power transmission zone of torque convertor becomes smaller as the torque converter gets nearer to a high speed ratio zone and a torque transmission capacity of the torque convertor therefore becomes smaller, so that it is impossible to make the best use of an engine performance.